This Mentored-Patient Oriented Research Career proposal will provide for a structured environment with expert mentorship that will allow Dr. Brian Smith to develop into an independent clinical researcher. Antibiotics are the most commonly used medications in hospitalized infants; however, dosing for infants is often extrapolated from data obtained in older children and adults. Meropenem and cefazolin are two commonly used antimicrobials for which little PK data are available. Dr. Smith will use an integrative approach to efficiently investigate the PK of these two agents in infants. This approach will include: application of scavenge sampling methodologies, advanced PK-PD modeling, integration of standard of care laboratory monitoring into the trial design, and use of clinical opportunities to collect samples. This proposal will capitalize on the unique opportunities provided by an NICHD-funded trial, Meropenem Pediatric Off- Label Study (PI Benjamin). Dr. Smith will also have access to the resources provided through the Pediatric Pharmacology Research Unit (PPRU); this includes the involvement of Drs. Benjamin (PI North Carolina Collaborative PPRU), Capparelli (PI University of San Diego PPRU), and McCracken (PI University Texas Southwestern PPRU). The proposal also benefits from the infrastructure of the Duke Neonatal Perinatal Research Institute (Goldberg), the Duke Clinical Research Institute (Benjamin) and the School of Pharmacy at UNC (Thakker). The strengths of the mentorship team include extensive clinical research experience; internationally recognized thought leadership in trial design, research methods, and pharmacology; and a successful history of mentorship of junior faculty. Dr. Smith's long term goal is to develop a clinical trial group specializing in evaluating therapeutic agents in critically ill infants. This K23 proposal will allow him the opportunity to master PK/PD modeling and simulation techniques and to refine clinical trial methodologies in order to maximize information gained from the limited samples available in premature infants. These skills will be developed through a combination of formal didactic training in pharmacology and biostatics, and from mentorship from nationally recognized experts in clinical trials and pediatric pharmacology. RELEVANCE (See instructions): Despite a neonatal medicine's long history of catastrophic adverse events resulting from inadequate study of drugs prior to their widespread use, the majority of antimicrobials used in infants have undergone insufficient study in infants. This proposal will use an integrative approach to efficiently investigate the PK of meropenem and cefazolin, two agents commonly used in infants, using the following methods: application of scavenge sampling methodologies, advanced PK-PD modeling, and use of clinical opportunities to collect samples.